The Huwan high-pressure(HP)metamorphic zone is a key region to investigate the evolution process and timing of the Qinling-Dabieshan-Sulu orogenic belt.However,the timing of eclogite-facies metamorphism in this zone has not been well constrained.In order to constrain the time of eclogite-facies metamorphism,zircons from a metasediment sample HXD98-9 near Xiongdian were selected for LA-ICPMS U-Pb dating and trace element analysis.Metamorphic zircons are characterized by weak or none zoning,low Th/U ratios,low and/or flat HREE patterns,and an insignificantly negative Eu anomaly.These reflect that the metamorphc zircons crystallized with the presence of garnet and the absence of plagioclase feldspar,which occurred in eclogite-facies conditions.The weighted mean 206Pb/238U age of 310±3Ma for these metamorphic zircons is thus the best estimated age of the eclogite-facies metamorphism in this HP metamorphic zone.Three groups of U-Pb age were obtained from the inherited magmatic zircons,ranging of(400±5Ma)-(419± 5Ma),(426±5Ma)-(449±5Ma),and(496±5Ma)-(524±7Ma),respectively.One inherited grain has a U-Pb age of 580.7±7.3Ma.These indicate that the inherited zircons were mostly derived from southern part of the North China block,while some from the Yangtze block.

ZHANG Zhen-guo1,2,3,FANG Nian-qiao4,DU Yuan-sheng1,GAO Lian-feng3,YANG Sheng-xiong5,LIU Jian5,SONG Cheng-bing51.Faculty of Earth Sciences,China University of Geosciences,Wuhan430074,China2.CAS Key Laboratory of Marginal Sea Geology,South China Sea Institute of Oceanology,Chinese Academy of Sciences,Guangzhou510301,China3.College of Resources and Environment,Hebei Polytechnic University,Tangshan063009,China4.School of Ocean Sciences,China University of Geosciences,Beijing100083,China5.Guangzhou Marine Geological Survey,The Ministry of Land and Resources of P.R.C.,Guangzhou510075,China;Geochemical Characteristics and Their Causative Mechanism of Polymetallic Nodules from the Northwest Continental Margin of the South China Sea[J];Earth Science(Journal of China University of Geosciences);2009-06